Conventionally, an evaporated fuel processing device is widely used. This evaporated fuel processing device is arranged to temporarily adsorb an evaporated fuel generated in a fuel tank of a vehicle to a canister using adsorption material (adsorbent) such as activated carbon, then to purge combustion components from the canister by introduction of flesh air during driving of the internal combustion engine, and to introduce it into an intake system of the internal combustion engine. In recent years, as disclosed in a Japanese Patent No. 5373459, there are proposed various evaporated fuel processing devices each of which includes a blocking valve disposed in an evaporated fuel passage connecting the fuel tank and the canister, and each of which is arranged to maintain the fuel tank in a sealed state by basically closing the blocking valve except for at the refueling.
In the above-described evaporated fuel processing device of the sealed type fuel tank which includes the blocking valve, the pressure within the fuel tank may reach the negative pressure while the blocking valve is closed. Japanese Patent No. 5373459 proposes that the blocking valve is opened to introduce the atmospheric pressure through the canister into the fuel tank when the tank internal pressure reaches the negative pressure.
However, in the blocking valve, a relatively large electromagnetic valve is used so as to attain a smooth refueling. Accordingly, when the blocking valve is opened when the fuel tank reaches the negative pressure like Japanese Patent No. 5373459, the gas suddenly flows toward the fuel tank. Consequently, abnormal noise is generated in accordance with the sudden pressure variation within the fuel tank and the flow of the gas.